The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Alain Roques - One of the best experts on this subject based on the ideXlab platform.
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Can we trust in historical data to disentangle the evolutionary history of introduction? Input of a genetic approach to compare the invasion histories of two seed Chalcids (Megastigmus sp.) in France
2018Co-Authors: Marie-anne Auger-rozenberg, Alain Roques, Thomas Boivin, Carole KerdelhuéAbstract:In recent decades, the number of introduced species has increased due to the development of human activities such as trades and transports. Insect species developing within fruits or seeds are particularly difficult to detect and may have a high invasive potential. The insect genus Megastigmus is a group of micro-hymenoptera that mostly develop in seeds. Several species of Megastigmus have been accidentally introduced in different parts of the world through the exchange of seeds carrying hidden Megastigmus larvae. Among these species, two were introduced in France a century apart: the Douglas fir seed Chalcid, Megastigmus spermotrophus, was introduced from North America to Europe at the end of XIXth century, and the cedar seed Chalcid, Megastigmus schimitscheki, was observed for the first time in southeastern France in the early 1990’s. To disentangle the evolutionary history of these introductions, we used two complementary approaches: (i) reviewing available historical data on the traceability of imported seed lots, and (ii) studying the patterns of genetic diversity of the invasive wasps in their native range compared to the invasive range. We combined mitochondrial sequences and nuclear microsatellites to characterize several populations from both the areas, and our results suggest that we can trust the historical data for the Douglas-fir seed Chalcid (i.e. sourced from the North American coast) even if some genetic data indicate that the history in the introduced range is likely complex. On the other hand, genetic results demonstrate an unambiguously Cypriot origin for the cedar seed Chalcid, although the available historical data strongly suggested that Turkey could be the most plausible source area. We conclude that historical data may provide incomplete, sparse or misleading information on invasion history, and genetic analyses are essential to reconstruct the whole history.
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Seed wasp invasions promoted by unregulated seed trade affect vegetal and animal biodiversity
Integrative Zoology, 2012Co-Authors: Marie-anne Auger-rozenberg, Alain RoquesAbstract:Cone and seed insects are considered the most important predators of tree seeds during the pre-dispersal phase of development. Among them, exotic seed Chalcids in the genus Megastigmus invaded Europe as a result of the rapidly-increasing and mostly unregulated seed trade for afforestation and ornamental plantations. Unlike their economic impact in seed orchards, until recently, little attention was paid to the ecological impact of these insects. In the present study, selected case studies of alien Megastigmus spp. were considered to assess their specific impact on the potential of natural regeneration of native woody plants and on the native entomofauna competing for seed resource. We re-analyzed data from former studies that did not focus on these ecological interactions and, here, present previously unpublished results. Seeds of Douglas-fir, true cedars, true firs and wild roses were sampled all over Europe, and the relative importance of the native and invasive Chalcid species was assessed as well as their specific impact on seed yield. In most cases, the recent arrival of alien Chalcids resulted in a significant decrease in the regeneration potential of the host trees. In the absence of competitors, alien Chalcids occupied the entire seed niche in Douglas-fir, but their impact tended to decrease after the arrival of invasive seed bugs. In firs, alien Chalcids tended to displace the native Chalcids, but not in wild roses and cedars, where their damage was increasing. Different biological traits that might explain invasive success of alien Chalcids are discussed. However, no general invasive patterns seem to exist.
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Modelling the impact of an invasive insect via reaction-diffusion
2007Co-Authors: Lionel Roques, Marie-anne Auger-rozenberg, Alain RoquesAbstract:An exotic, specialist seed Chalcid, Megastigmus schimitscheki, has been introduced along with its cedar host seeds from Turkey to southeastern France during the early 1990s. It is now expanding in plantations of Atlas Cedar (Cedrus atlantica). We propose a two-dimensional reaction-diffusion model to predict the expansion and impacts of this insect. Two main diffusion operators, of Fokker-Planck and Fickian types, are tested. We show that taking account of spatial heterogeneity, and choosing the appropriate operator are critical for obtaining good predictions.
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Oviposition Sites of the Cypress Seed Bug Orsillus maculatus and Response of the Egg Parasitoid Telenomus gr. Floridanus
BioControl, 2006Co-Authors: Gaelle Rouault, Andrea Battisti, Alain RoquesAbstract:Phytophagous insects have many strategies to escape parasitoids, for example by hiding eggs into plant tissues, but oviposition in holes made by another insect is rather scarce. The cypress seed bug Orsillus maculatus Fieber (Heteroptera: Lygaeidae) is strictly dependent on the availability of cones of Cupressus sempervirens L. to oviposit. Females lay eggs either in exit holes cut through the cone scale by emerging adults of the cypress seed Chalcid, Megastigmus wachtli Seitner (Hymenoptera: Torymidae), or on the inner side of scales of partly open cones. A recently discovered egg parasitoid belonging to the genus Telenomus has been shown to attack bug eggs in both oviposition sites. In this paper we investigated the parasitoid performance according to oviposition sites. Field samplings were conducted in two evergreen cypress orchards located in the south of France. The distribution and condition of the egg patches were compared between the two locations and oviposition sites. Seed bugs preferred to oviposit in emergence holes of M. wachtli , and parasitoid performance was higher in eggs laid on cone scales. The Chalcid emergence holes seemed to ensure bug eggs with enemy-free space. Oviposition site selection could be an adaptive strategy to escape parasitoid attack.
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Oviposition strategies of conifer seed Chalcids in relation to host phenology
Naturwissenschaften, 2004Co-Authors: Gaelle Rouault, Jean-noël Candau, Jean Turgeon, Alain Roques, Patrick Von AderkasAbstract:Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed Chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed Chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus . Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect–plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus . The evidence from our compilation suggests that seed Chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus , whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed Chalcid infesting Pinaceae on seed production.
S. Boivin - One of the best experts on this subject based on the ideXlab platform.
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Competition between exotic and native insects for seed resources in trees of a Mediterranean forest ecosystem
Biological Invasions, 2004Co-Authors: J.p. Fabre, Marie-anne Auger-rozenberg, Alain Chalon, S. Boivin, Alain RoquesAbstract:The seeds of both cedar-of-Lebanon (Cedrus libani) and Cyprus cedar (Cedrus brevifolia) are attacked in their natural range by a specialised Chalcid, Megastigmus schimitscheki. From 1995 to 1999, seeds were screened for insect damage in the main cedar plantations of southern France, as well as in the stands where cedar is mixed with firs (Abies spp.). X-rays were used to identify Chalcid-infested seeds from which the insects were then reared. The surveys revealed the presence of M. schimitscheki in all the stands of Atlas cedar, Cedrus atlantica, planted at Mt Ventoux, southeastern France. The Chalcid also infested seeds of an exotic fir, Abies pinsapo, planted in the same area. However, it has not yet reached the cedar plantations in southwestern France, where the seeds are colonised by a related exotic insect, Megastigmus pinsapinis, originating from North Africa. The latter species was common in cedar seeds at Mt Ventoux in the early 1990s but seems to have been supplanted by M. schimitscheki in the invasion zone. A native Chalcid species, Megastigmus suspectus, was also shown to have shifted to a slight extent from a native fir, A. alba, onto cedar. The presence of three Chalcid species competing for cedar seed resources may result in a substantial decline of the regeneration potential of that tree species. At Mt Ventoux, up to 92.6% of the cedar seeds were attacked, with 86.8% due to M. schimitscheki. The survey also revealed the widespread presence of another North American Chalcid, Megastigmus rafni, in the fir stands of southern France.
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Characterization of microsatellite loci in a seed Chalcid, Megastigmus spermotrophus (Hymenoptera: Torymidae)
Molecular Ecology Notes, 2003Co-Authors: S. Boivin, Carole Kerdelhué, M. A. Rozenberg, M. L. Cariou, Alain RoquesAbstract:Highly polymorphic microsatellite markers can supply demographic information on founder events and range expansion following initial introduction of invasive insect species. Six microsatellite loci were isolated from a partial DNA library in order to study the invasion patterns of a seed Chalcid, Megastigmus spermotrophus, introduced to Europe and New Zealand. Allelic diversity at all described loci was high, ranging from 17 to 30 alleles per locus. All six loci were successfully amplified in 15 congeneric species.
Marie-anne Auger-rozenberg - One of the best experts on this subject based on the ideXlab platform.
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Can we trust in historical data to disentangle the evolutionary history of introduction? Input of a genetic approach to compare the invasion histories of two seed Chalcids (Megastigmus sp.) in France
2018Co-Authors: Marie-anne Auger-rozenberg, Alain Roques, Thomas Boivin, Carole KerdelhuéAbstract:In recent decades, the number of introduced species has increased due to the development of human activities such as trades and transports. Insect species developing within fruits or seeds are particularly difficult to detect and may have a high invasive potential. The insect genus Megastigmus is a group of micro-hymenoptera that mostly develop in seeds. Several species of Megastigmus have been accidentally introduced in different parts of the world through the exchange of seeds carrying hidden Megastigmus larvae. Among these species, two were introduced in France a century apart: the Douglas fir seed Chalcid, Megastigmus spermotrophus, was introduced from North America to Europe at the end of XIXth century, and the cedar seed Chalcid, Megastigmus schimitscheki, was observed for the first time in southeastern France in the early 1990’s. To disentangle the evolutionary history of these introductions, we used two complementary approaches: (i) reviewing available historical data on the traceability of imported seed lots, and (ii) studying the patterns of genetic diversity of the invasive wasps in their native range compared to the invasive range. We combined mitochondrial sequences and nuclear microsatellites to characterize several populations from both the areas, and our results suggest that we can trust the historical data for the Douglas-fir seed Chalcid (i.e. sourced from the North American coast) even if some genetic data indicate that the history in the introduced range is likely complex. On the other hand, genetic results demonstrate an unambiguously Cypriot origin for the cedar seed Chalcid, although the available historical data strongly suggested that Turkey could be the most plausible source area. We conclude that historical data may provide incomplete, sparse or misleading information on invasion history, and genetic analyses are essential to reconstruct the whole history.
-
Seed wasp invasions promoted by unregulated seed trade affect vegetal and animal biodiversity
Integrative Zoology, 2012Co-Authors: Marie-anne Auger-rozenberg, Alain RoquesAbstract:Cone and seed insects are considered the most important predators of tree seeds during the pre-dispersal phase of development. Among them, exotic seed Chalcids in the genus Megastigmus invaded Europe as a result of the rapidly-increasing and mostly unregulated seed trade for afforestation and ornamental plantations. Unlike their economic impact in seed orchards, until recently, little attention was paid to the ecological impact of these insects. In the present study, selected case studies of alien Megastigmus spp. were considered to assess their specific impact on the potential of natural regeneration of native woody plants and on the native entomofauna competing for seed resource. We re-analyzed data from former studies that did not focus on these ecological interactions and, here, present previously unpublished results. Seeds of Douglas-fir, true cedars, true firs and wild roses were sampled all over Europe, and the relative importance of the native and invasive Chalcid species was assessed as well as their specific impact on seed yield. In most cases, the recent arrival of alien Chalcids resulted in a significant decrease in the regeneration potential of the host trees. In the absence of competitors, alien Chalcids occupied the entire seed niche in Douglas-fir, but their impact tended to decrease after the arrival of invasive seed bugs. In firs, alien Chalcids tended to displace the native Chalcids, but not in wild roses and cedars, where their damage was increasing. Different biological traits that might explain invasive success of alien Chalcids are discussed. However, no general invasive patterns seem to exist.
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Modelling the impact of an invasive insect via reaction-diffusion
2007Co-Authors: Lionel Roques, Marie-anne Auger-rozenberg, Alain RoquesAbstract:An exotic, specialist seed Chalcid, Megastigmus schimitscheki, has been introduced along with its cedar host seeds from Turkey to southeastern France during the early 1990s. It is now expanding in plantations of Atlas Cedar (Cedrus atlantica). We propose a two-dimensional reaction-diffusion model to predict the expansion and impacts of this insect. Two main diffusion operators, of Fokker-Planck and Fickian types, are tested. We show that taking account of spatial heterogeneity, and choosing the appropriate operator are critical for obtaining good predictions.
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Competition between exotic and native insects for seed resources in trees of a Mediterranean forest ecosystem
Biological Invasions, 2004Co-Authors: J.p. Fabre, Marie-anne Auger-rozenberg, Alain Chalon, S. Boivin, Alain RoquesAbstract:The seeds of both cedar-of-Lebanon (Cedrus libani) and Cyprus cedar (Cedrus brevifolia) are attacked in their natural range by a specialised Chalcid, Megastigmus schimitscheki. From 1995 to 1999, seeds were screened for insect damage in the main cedar plantations of southern France, as well as in the stands where cedar is mixed with firs (Abies spp.). X-rays were used to identify Chalcid-infested seeds from which the insects were then reared. The surveys revealed the presence of M. schimitscheki in all the stands of Atlas cedar, Cedrus atlantica, planted at Mt Ventoux, southeastern France. The Chalcid also infested seeds of an exotic fir, Abies pinsapo, planted in the same area. However, it has not yet reached the cedar plantations in southwestern France, where the seeds are colonised by a related exotic insect, Megastigmus pinsapinis, originating from North Africa. The latter species was common in cedar seeds at Mt Ventoux in the early 1990s but seems to have been supplanted by M. schimitscheki in the invasion zone. A native Chalcid species, Megastigmus suspectus, was also shown to have shifted to a slight extent from a native fir, A. alba, onto cedar. The presence of three Chalcid species competing for cedar seed resources may result in a substantial decline of the regeneration potential of that tree species. At Mt Ventoux, up to 92.6% of the cedar seeds were attacked, with 86.8% due to M. schimitscheki. The survey also revealed the widespread presence of another North American Chalcid, Megastigmus rafni, in the fir stands of southern France.
Patrick Von Aderkas - One of the best experts on this subject based on the ideXlab platform.
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Oviposition strategies of conifer seed Chalcids in relation to host phenology
Naturwissenschaften, 2004Co-Authors: Gaelle Rouault, Jean-noël Candau, Jean Turgeon, Alain Roques, Patrick Von AderkasAbstract:Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed Chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed Chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus . Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect–plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus . The evidence from our compilation suggests that seed Chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus , whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed Chalcid infesting Pinaceae on seed production.
Gaelle Rouault - One of the best experts on this subject based on the ideXlab platform.
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Oviposition Sites of the Cypress Seed Bug Orsillus maculatus and Response of the Egg Parasitoid Telenomus gr. Floridanus
BioControl, 2006Co-Authors: Gaelle Rouault, Andrea Battisti, Alain RoquesAbstract:Phytophagous insects have many strategies to escape parasitoids, for example by hiding eggs into plant tissues, but oviposition in holes made by another insect is rather scarce. The cypress seed bug Orsillus maculatus Fieber (Heteroptera: Lygaeidae) is strictly dependent on the availability of cones of Cupressus sempervirens L. to oviposit. Females lay eggs either in exit holes cut through the cone scale by emerging adults of the cypress seed Chalcid, Megastigmus wachtli Seitner (Hymenoptera: Torymidae), or on the inner side of scales of partly open cones. A recently discovered egg parasitoid belonging to the genus Telenomus has been shown to attack bug eggs in both oviposition sites. In this paper we investigated the parasitoid performance according to oviposition sites. Field samplings were conducted in two evergreen cypress orchards located in the south of France. The distribution and condition of the egg patches were compared between the two locations and oviposition sites. Seed bugs preferred to oviposit in emergence holes of M. wachtli , and parasitoid performance was higher in eggs laid on cone scales. The Chalcid emergence holes seemed to ensure bug eggs with enemy-free space. Oviposition site selection could be an adaptive strategy to escape parasitoid attack.
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Oviposition strategies of conifer seed Chalcids in relation to host phenology
Naturwissenschaften, 2004Co-Authors: Gaelle Rouault, Jean-noël Candau, Jean Turgeon, Alain Roques, Patrick Von AderkasAbstract:Insects are considered the most important predators of seed cones, the female reproductive structures of conifers, prior to seed dispersal. Slightly more than 100 genera of insects are known to parasitize conifer seed cones. The most diverse (i.e., number of species) of these genera is Megastigmus (Hymenoptera: Torymidae), which comprises many important seed pests of native and exotic conifers. Seed Chalcids, Megastigmus spp., lay eggs inside the developing ovules of host conifers and, until recently, oviposition was believed to occur only in fertilized ovules. Ovule development begins just after pollination, but stops if cells are not fertilized. The morphological stage of cone development at the time of oviposition by seed Chalcids has been established for many species; however, knowledge of ovule development at that time has been documented for only one species, M. spermotrophus . Megastigmus spermotrophus oviposits in Douglas-fir ovules after pollination but before fertilization. Unlike the unfertilized ovules, those containing a M. spermotrophus larva continue to develop, whether fertilized or not, stressing the need to broaden our understanding of the insect–plant interactions for this entire genus. To achieve this task, we reviewed the scientific literature and assembled information pertaining to the timing of oviposition and to the pollination and fertilization periods of their respective host(s). More specifically, we were searching for circumstantial evidence that other species of Megastigmus associated with conifers could behave (i.e., oviposit before ovule fertilization) and impact on female gametophyte (i.e., prevent abortion) like M. spermotrophus . The evidence from our compilation suggests that seed Chalcids infesting Pinaceae may also oviposit before ovule fertilization, just like M. spermotrophus , whereas those infesting Cupressaceae seemingly oviposit after ovule fertilization. Based on this evidence, we hypothesize that all species of Megastigmus associated with Pinaceae can oviposit in unfertilized ovules, whereas those exploiting Cupressaceae cannot, and thus oviposit only in already fully developed fertilized seeds. Furthermore, we predict that the presence of a larva in unfertilized ovules of all Pinaceae will influence the development of the female gametophyte by preventing its abortion. This influence on the Pinaceae can be interpreted as an ability to parasitize any of the potential seeds present in a seed cone, and as such represents a much more efficient oviposition strategy than searching and locating only fertilized seeds. Concomitantly, this ability has likely led to an overestimation of the impact of the species of seed Chalcid infesting Pinaceae on seed production.